Abstract Determination of Transforming Growth Factor-? type I receptor (TGF-?RI) Signaling Targets in Activated T Cells In the adaptive immune system Transforming Growth Factor-? (TGF-?) signaling has non-redundant functions in T cell regulation in homeostasis and disease states1. Specifically, TGF-? signaling in T cells facilitates the maintenance of tolerance to self-antigens and environmental antigens 2. Additionally, TGF-? mediated suppression of T cell activation and promotes the tumor persistence and metastasis3. TGF-? signaling also acts on activated T cells to promote the differentiation of TGF-? dependent T helper (Th) subsets with effector or regulatory functions such as Th9, Th17, Th22 and Tregs, and inhibit Th1 or Th2 differentiation2,4,5. Despite these pleiotropic roles of TGF-? signaling in T cell regulation, the molecular mechanism by which TGF-? signaling controls T cell differentiation and suppression remain poorly understood4. Knowing this, our goal is to elucidate the direct targets of TGF-? signaling in activated T cells. Theses studies could inform the design of therapeutics that modulate T cell responses to promote tumor regression or inhibit autoimmune/hyperimmune diseases. To achieve our goal, this we generated a TGF-? type I receptor (TGF- ?RI) deficient Jurkat T cell line using the CRISPR/cas9 genome editing system. Preliminary data characterizing the TGF-?RI deficient Jurkat T cell line suggest that TGF-?RI signaling suppresses some of the activation-induced proteins it also enhances others, especially those involved in co-stimulation of T cells. Specifically, we observe that upon stimulation of our TGF-?RI deficient Jurkat T cell line there is a highly enhanced level of CD25, CD69, IL-2 and tumor TNF-?, and expressed reduced levels of OX40, CD154, PD-1 and ICOS compared to Jurkat cas9. We also observe that there is highly elevated activity of activator protein-1 (AP-1) and there is constitutive activation of jun- amino-terminal kinase (JNK) compared to Jurkat cas9. Finally, we determined that the phosphatase that downregulates the activation of JNK, MAP kinase phosphatase-1 (MKP-1), shows a substantial decrease in the phosphorylated active form. Therefore, in contrast to the previously known roles of TGF-?RI signaling, our preliminary demonstrate that TGF-?RI signaling has an inhibitory role in JNK activation in T cells. This proposed study seeks to determine the structure-function relationship between TGF-?RI and the regulation of cytokines and activation induced surface marker gene expression in Jurkat T cells and to determine the TGF-?RI signaling pathway upstream of Jun-amino-terminal kinase (JNK) activation in T cells.